Index: lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- lib/Target/PowerPC/PPCISelLowering.cpp
+++ lib/Target/PowerPC/PPCISelLowering.cpp
@@ -5147,10 +5147,30 @@
   };
 
   const unsigned NumGPRs = array_lengthof(GPR);
-  const unsigned NumFPRs = 13;
+  const unsigned NumFPRs = useSoftFloat() ? 0 : 13;
   const unsigned NumVRs  = array_lengthof(VR);
   const unsigned NumQFPRs = NumFPRs;
 
+  // On ELFv2, we can avoid allocating the parameter area if all the arguments 
+  // can be passed to the callee in registers.
+  // For the fast calling convention, there is another check below.
+  // Note: keep consistent with LowerFormalArguments_64SVR4()
+  bool HasParameterArea = !isELFv2ABI || isVarArg || CallConv == CallingConv::Fast;
+  if (!HasParameterArea) {
+    unsigned ParamAreaSize = NumGPRs * PtrByteSize;
+    unsigned AvailableFPRs = NumFPRs;
+    unsigned AvailableVRs = NumVRs;
+    unsigned NumBytesTmp = NumBytes;
+    for (unsigned i = 0; i != NumOps; ++i) {
+      if (Outs[i].Flags.isNest()) continue;
+      if (CalculateStackSlotUsed(Outs[i].VT, Outs[i].ArgVT, Outs[i].Flags,
+                                PtrByteSize, LinkageSize, ParamAreaSize,
+                                NumBytesTmp, AvailableFPRs, AvailableVRs,
+                                Subtarget.hasQPX()))
+        HasParameterArea = true;
+    }
+  }
+
   // When using the fast calling convention, we don't provide backing for
   // arguments that will be in registers.
   unsigned NumGPRsUsed = 0, NumFPRsUsed = 0, NumVRsUsed = 0;
@@ -5218,13 +5238,18 @@
 
   unsigned NumBytesActuallyUsed = NumBytes;
 
-  // The prolog code of the callee may store up to 8 GPR argument registers to
+  // In the old ELFv1 ABI, 
+  // the prolog code of the callee may store up to 8 GPR argument registers to
   // the stack, allowing va_start to index over them in memory if its varargs.
   // Because we cannot tell if this is needed on the caller side, we have to
   // conservatively assume that it is needed.  As such, make sure we have at
   // least enough stack space for the caller to store the 8 GPRs.
-  // FIXME: On ELFv2, it may be unnecessary to allocate the parameter area.
-  NumBytes = std::max(NumBytes, LinkageSize + 8 * PtrByteSize);
+  // In the ELFv2 ABI, we allocate the parameter area iff a callee 
+  // really requires memory operands, e.g. a vararg function.
+  if (HasParameterArea)
+    NumBytes = std::max(NumBytes, LinkageSize + 8 * PtrByteSize);
+  else 
+    NumBytes = LinkageSize;
 
   // Tail call needs the stack to be aligned.
   if (getTargetMachine().Options.GuaranteedTailCallOpt &&
@@ -5443,6 +5468,8 @@
         if (CallConv == CallingConv::Fast)
           ComputePtrOff();
 
+        assert(HasParameterArea && 
+               "parameter area must exist to pass an argument in memory");
         LowerMemOpCallTo(DAG, MF, Chain, Arg, PtrOff, SPDiff, ArgOffset,
                          true, isTailCall, false, MemOpChains,
                          TailCallArguments, dl);
@@ -5528,6 +5555,8 @@
           PtrOff = DAG.getNode(ISD::ADD, dl, PtrVT, PtrOff, ConstFour);
         }
 
+        assert(HasParameterArea && 
+               "parameter area must exist to pass an argument in memory");
         LowerMemOpCallTo(DAG, MF, Chain, Arg, PtrOff, SPDiff, ArgOffset,
                          true, isTailCall, false, MemOpChains,
                          TailCallArguments, dl);
@@ -5562,6 +5591,8 @@
       // GPRs when within range.  For now, we always put the value in both
       // locations (or even all three).
       if (isVarArg) {
+        assert(HasParameterArea && 
+               "parameter area must exist if we have a varargs call");
         // We could elide this store in the case where the object fits
         // entirely in R registers.  Maybe later.
         SDValue Store =
@@ -5594,6 +5625,8 @@
         if (CallConv == CallingConv::Fast)
           ComputePtrOff();
 
+        assert(HasParameterArea && 
+               "parameter area must exist to pass an argument in memory");
         LowerMemOpCallTo(DAG, MF, Chain, Arg, PtrOff, SPDiff, ArgOffset,
                          true, isTailCall, true, MemOpChains,
                          TailCallArguments, dl);
@@ -5614,6 +5647,8 @@
     case MVT::v4i1: {
       bool IsF32 = Arg.getValueType().getSimpleVT().SimpleTy == MVT::v4f32;
       if (isVarArg) {
+        assert(HasParameterArea && 
+               "parameter area must exist if we have a varargs call");
         // We could elide this store in the case where the object fits
         // entirely in R registers.  Maybe later.
         SDValue Store =
@@ -5646,6 +5681,8 @@
         if (CallConv == CallingConv::Fast)
           ComputePtrOff();
 
+        assert(HasParameterArea && 
+               "parameter area must exist to pass an argument in memory");
         LowerMemOpCallTo(DAG, MF, Chain, Arg, PtrOff, SPDiff, ArgOffset,
                          true, isTailCall, true, MemOpChains,
                          TailCallArguments, dl);
@@ -5660,7 +5697,8 @@
     }
   }
 
-  assert(NumBytesActuallyUsed == ArgOffset);
+  assert((!HasParameterArea || NumBytesActuallyUsed == ArgOffset) &&
+         "mismatch in size of parameter area");
   (void)NumBytesActuallyUsed;
 
   if (!MemOpChains.empty())
Index: test/CodeGen/PowerPC/stacksize.ll
===================================================================
--- /dev/null
+++ test/CodeGen/PowerPC/stacksize.ll
@@ -0,0 +1,86 @@
+; For ELFv2 ABI, we can avoid allocating the parameter area in the stack frame of the caller function
+; if all the arguments can be passed to the callee in registers.
+; For ELFv1 ABI, we always need to allocate the parameter area.
+
+; Tests for ELFv2 ABI
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu -target-abi elfv2 < %s | FileCheck %s -check-prefix=PPC64-ELFV2
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64-unknown-linux-gnu -target-abi elfv2 < %s | FileCheck %s -check-prefix=PPC64-ELFV2
+
+; Tests for ELFv1 ABI
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu -target-abi elfv1 < %s | FileCheck %s -check-prefix=PPC64-ELFV1
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64-unknown-linux-gnu -target-abi elfv1 < %s | FileCheck %s -check-prefix=PPC64-ELFV1
+
+; If the callee has at most eight integer args, parameter area can be ommited for ELFv2 ABI.
+
+; PPC64-ELFV2-LABEL: WithoutParamArea1:
+; PPC64-ELFV2-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV2: stdu 1, -32(1)
+; PPC64-ELFV2: addi 1, 1, 32
+; PPC64-ELFV2-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV1-LABEL: WithoutParamArea1:
+; PPC64-ELFV1-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV1: stdu 1, -112(1)
+; PPC64-ELFV1: addi 1, 1, 112
+; PPC64-ELFV1-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
+define signext i32 @WithoutParamArea1(i32 signext %a) local_unnamed_addr #0 {
+entry:
+  %call = tail call signext i32 @onearg(i32 signext %a) #2
+  ret i32 %call
+}
+
+; PPC64-ELFV2-LABEL: WithoutParamArea2:
+; PPC64-ELFV2-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV2: stdu 1, -32(1)
+; PPC64-ELFV2: addi 1, 1, 32
+; PPC64-ELFV2-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV1-LABEL: WithoutParamArea2:
+; PPC64-ELFV1-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV1: stdu 1, -112(1)
+; PPC64-ELFV1: addi 1, 1, 112
+; PPC64-ELFV1-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
+define signext i32 @WithoutParamArea2(i32 signext %a) local_unnamed_addr #0 {
+entry:
+  %call = tail call signext i32 @eightargs(i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a) #2
+  ret i32 %call
+}
+
+; If the callee has more than eight integer args or variable number of args, 
+; parameter area cannot be ommited even for ELFv2 ABI
+
+; PPC64-ELFV2-LABEL: WithParamArea1:
+; PPC64-ELFV2-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV2: stdu 1, -96(1)
+; PPC64-ELFV2: addi 1, 1, 96
+; PPC64-ELFV2-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV1-LABEL: WithParamArea1:
+; PPC64-ELFV1-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV1: stdu 1, -112(1)
+; PPC64-ELFV1: addi 1, 1, 112
+; PPC64-ELFV1-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
+define signext i32 @WithParamArea1(i32 signext %a) local_unnamed_addr #0 {
+entry:
+  %call = tail call signext i32 (i32, ...) @varargs(i32 signext %a, i32 signext %a) #2
+  ret i32 %call
+}
+
+; PPC64-ELFV2-LABEL: WithParamArea2:
+; PPC64-ELFV2-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV2: stdu 1, -112(1)
+; PPC64-ELFV2: addi 1, 1, 112
+; PPC64-ELFV2-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV1-LABEL: WithParamArea2:
+; PPC64-ELFV1-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
+; PPC64-ELFV1: stdu 1, -128(1)
+; PPC64-ELFV1: addi 1, 1, 128
+; PPC64-ELFV1-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
+define signext i32 @WithParamArea2(i32 signext %a) local_unnamed_addr #0 {
+entry:
+  %call = tail call signext i32 @nineargs(i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a) #2
+  ret i32 %call
+}
+
+declare signext i32 @onearg(i32 signext) local_unnamed_addr #1
+declare signext i32 @eightargs(i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext) local_unnamed_addr #1
+declare signext i32 @nineargs(i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext) local_unnamed_addr #1
+declare signext i32 @varargs(i32 signext, ...) local_unnamed_addr #1
+